Radio-transparent real-time dosimeter for interventional radiological procedures

ABSTRACT

A method of measuring in real time a dose of radiological radiation absorbed by a region under inspection subjected to a flux of radiological radiation, the method comprising the steps consisting in: a) detecting the incident radiation at at least one point of the region under inspection using at least a first bundle of measurement optical fibers ( 2 ) containing at least one fiber placed in said region under inspection and adapted to generate a light signal on receiving radiological radiation; b) measuring said light signal away from the region under inspection after it has been transmitted along the measurement optical fiber; and c) determining the dose of radiological radiation received by said measurement optical fiber on the basis of said light signal.

BACKGROUND OF THE DISCLOSURE

The present invention relates to a method of measuring in real time thedose of radiological radiation received by a region that is subjected toa flux of radiological radiation.

FIELD OF THE INVENTION

It is important to know the cutaneous dose received by a patient in realtime during an examination, e.g. during vascular radiologicalexamination, or during interventional cardiology examination, sincecutaneous irradiation can lead to irreversible dermatological effectsthat, at present, are observed only a posteriori.

Document EP 1 167 999 describes a real-time dosimeter based on a matrixof silicon detectors. That dosimeter enables the received dose to bemapped by processing the signal delivered by each matrix cell of thedetector, but it is effective only for energies of mega electron volt(MeV) order, which is an energy threshold that is well above theenergies used during conventional radiological examinations. Forconventional radiological procedures, document WO 00/62 092 describes adosimeter connected via an optical fiber to a detector. That dosimeterenables a dose of radiation received by a very precisely localized zoneto be determined. Nevertheless, that device does not enable a detailedmap to be obtained of irradiation in the zone under examination.

Another technique enabling the dose received by a zone subjected toradiation during an examination to be obtained in real time consists infinding the dose for said zone by calculation on the basis of the dosemeasured at the output from a radiation emitter device. Nevertheless,that method is not suitable for determining an irradiation map since thegeometry of the irradiation is subject to change.

SUMMARY OF THE DISCLOSURE

A particular object of the present invention is to mitigate thosedrawbacks. To this end, the invention provides a method of measuring inreal time a radiological radiation dose absorbed by a region underinspection subjected to a flux of radiological radiation, the methodcomprising the steps consisting in:

a) detecting the incident radiation at at least one point of the regionunder inspection using at least a first bundle of measurement opticalfibers containing at least one fiber placed in said region underinspection and adapted to generate a light signal on receivingradiological radiation;

b) measuring said light signal away from the region under inspectionafter it has been transmitted along the measurement optical fiber; and

c) determining the dose of radiological radiation received by saidmeasurement optical fiber on the basis of said light signal.

By means of these dispositions, a signal is obtained that isrepresentative of the radiation transmitted through each of the opticalfibers, and as a function of the locations of said optical fibers, a mapcan be obtained of the radiation dose transmitted to the region underinspection. This dosimeter is also X-ray transparent since the signalprocessor apparatuses lie away from the region under inspection, thusenabling the practitioner to act without being impeded by the dosimeter.

In preferred embodiments of the invention, recourse may optionally behad to one or more of the following dispositions:

-   -   during step c), a position where the radiological radiation is        detected along said measurement optical fiber is determined, and        the dose of radiological radiation received at said position is        calculated as a function of at least one parameter F⁰ _(k)        specific to said optical fiber;    -   at least one parameter F⁰ _(k) is obtained by a preliminary        calibration step during which a dose of radiation is detected at        at least one point of the region under inspection by means of a        radiation detector that is not X-ray transparent;    -   step b) is performed using a detector device comprising at least        one cell, and the parameter F⁰ _(k) takes account of at least        the optical fiber and at least one cell of the detector device        associated with said fiber;    -   the first measurement optical fiber bundle extends in a first        direction, and step a) is also performed using a second optical        fiber bundle containing at least one second measurement optical        fiber adapted to generate a light signal on receiving        radiological radiation, and extending along a second direction        forming an angle with the first direction;    -   steps b) and c) are performed, for at least one overlap point        (i, j) between a first measurement optical fiber i of the first        bundle and a second measurement optical fiber j of the second        bundle, on the basis of the radiation detected at least by the        first optical fiber i of the fibers of the first bundle, of the        radiation detected by the second optical fiber j, and of the        position of said overlap point (i, j) along the second optical        fiber j;    -   the steps b) and c) are performed, at least for an overlap point        (i, j) between a first measurement optical fiber i of the first        bundle and a second measurement optical fiber j of the second        bundle, on the basis of the radiation detected at least by the        second optical fiber j of the fibers in the second bundle, of        the radiation detected by the first optical fiber i, and of the        position of said overlap point (i, j) along the first optical        fiber i;    -   the method further comprises a step d) consisting in emitting an        alarm signal if the accumulated received radiation dose exceeds        a pre-established threshold;    -   the method further comprises a step e) consisting in displaying        on a screen the dose of radiation received at at least one point        of the region under inspection;    -   the method further comprises a step f) consisting in detecting        the radiation transmitted through the region under inspection,        and in displaying on a screen the radiographic image as detected        in this way;    -   the radiographic image obtained in step f) and the image of the        received radiation dose as obtained in step e), are displayed on        the same screen;    -   at least steps a), b), and c) are repeated for a plurality of        points of the region under inspection, enabling a map to be        obtained of the dose received by the region under inspection;    -   at least steps a), b), and c) are repeated for a plurality of        measurement time intervals enabling time variation in the dose        received at at least one point of the region under inspection to        be obtained;    -   the radiation is generated by a pulsed source, and the        repetition of at least steps b) and c) is synchronized with said        source; and    -   at least steps a), b) and c) are performed for at least two        angles of incidence of the radiation, and combined use is made        of the received radiation doses as determined in step c) for        each of the angles of incidence.

In another aspect, the invention provides a device for real-timemeasurement of a dose of radiological radiation absorbed by a regionunder inspection subjected to a flux of radiological radiation, thedevice comprising:

-   -   a dosimeter comprising at least a first bundle of measurement        optical fibers containing at least one fiber placed in said        region under inspection and adapted to generate a light signal        on receiving radiological radiation in order to detect the        incident radiation at at least one point of the region under        inspection;    -   measurement means for measuring said light signal away from the        region under inspection after the light signal has been        transmitted along the measurement optical fiber; and    -   means for determining the dose of radiological radiation        received by said measurement optical fiber on the basis of said        light signal.

This device also comprises one or more of the following dispositions:

-   -   the light signal is transmitted to a detector device used for        measuring it, transmission taking place along the measurement        optical fiber used for detecting the radiation, said fiber        having a first end, and along at least one clear optical fiber        extending from a first end of the clear fiber that is connected        to the first end of the measurement optical fiber to a second        end of the clear fiber, which second end is placed facing the        detector device, and the means for determining the dose of        radiation received at said point of said measurement optical        fiber comprise a control unit containing parameters that are        specific to the optical fibers used;    -   the first fiber bundle is disposed along a first direction and        the dosimeter further comprises a second bundle of optical        fibers comprising at least one second measurement optical fiber        disposed in a second direction forming an angle with the first        direction;    -   each measurement optical fiber is comprised between two        optically-insulating sheets;    -   each measurement optical fiber is molded in a reflective resin        comprised between two optically-insulating sheets; and    -   at least one bundle of optical fibers is integrated in an        examination table.

In another aspect, the invention also provides a radiologicalinstallation comprising:

-   -   a dosimeter comprising at least one bundle having at least one        measurement optical fiber placed in a region under inspection,        and adapted to generate a light signal on receiving radiological        radiation, so as to enable the incident radiation to be detected        at at least one point of said region under inspection;    -   measurement means for measuring said light signal away from the        region under inspection after it has been transmitted along the        measurement optical fiber; and    -   means for determining the dose of radiological radiation        received by said measurement optical fiber on the basis of said        light signal, and further comprising:        -   a radiation generator;        -   a radiographic detector; and        -   means for displaying the radiation dose received, said means            also enabling radiographic images to be displayed of the            region under inspection as supplied by the radiographic            detector.

This installation may also comprise one or more of the followingdispositions:

-   -   the installation further comprises an examination table;    -   at least one bundle of measurement optical fibers is integrated        in the examination table; and    -   the installation further comprises at least one additional        device that is not integrated in the examination table, for        real-time measurement of a dose of radiological radiation        absorbed by a region under inspection subjected to a flux of        radiological radiation, the additional device comprising:        -   at least an additional first bundle comprising at least one            additional first measurement optical fiber placed in said            region under inspection and adapted to generate an            additional light signal on receiving radiological radiation,            in order to detect the incident radiation at at least one            point in said region under inspection;        -   additional measurement means for measuring said additional            light signal away from the region under inspection after it            has been transmitted along the additional measurement            optical fiber; and        -   additional means for determining the dose of radiological            radiation received by said additional measurement optical            fiber on the basis of said additional light signal.

Other aspects, objects, and advantages of the invention appear onreading the description of various embodiments given as non-limitingexamples.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can also be better understood with the help of thedrawings, in which:

FIG. 1 is a diagram showing the implementation of the method of theinvention;

FIG. 2 is an exploded view in perspective showing an example of adosimeter of the invention;

FIG. 3 shows the step of transmitting optical information in accordancewith the invention;

FIG. 4 shows a first embodiment of an installation implementing themethod of the invention; and

FIG. 5 shows a second embodiment of an installation enabling the methodof the invention to be implemented.

DETAILED DESCRIPTION OF THE DISCLOSURE

In the various figures, the same references are used to designateelements that are identical or similar.

In FIG. 1, a dosimeter 1 of rectangular or other shape comprises firstmeasurement fibers 2 extending along a first direction X of thedosimeter, and second measurement optical fibers 3 extending along asecond direction Y of the dosimeter. Each of these measurement opticalfibers 2 and 3 has a first end 5 connected to a clear fiber 6 and asecond end 4 that is optically closed or that is reflective. Each of theclear fibers 6 extends from a first end 14 of the clear fiber 6 where itis connected to the first end 5 of the measurement fiber 2, 3 to asecond end 15 of the clear fiber 6 where it is engaged with a detector9. The second end 15 of each clear fiber 6 can be mounted in arespective orifice 8 of an adapter 7 placed facing the detector 9 so asto ensure that the clear fiber 6 is properly positioned. By way ofexample, the detector 9 may be a multiple cell detector in which each ofthe cells 10 is placed facing one of the orifices 8 of the adapter 7. Ifradiation 11 coming from a source of radiation 18 passes through ameasurement optical fiber 2, 3 extending along the first or the seconddirection of the dosimeter, then a light signal is conveyed along themeasurement fiber and along the clear fiber that is connected theretountil it reaches the detector 9, possibly via the corresponding orifices8 in the adapter 7. With a weak signal, it may be advantageous to causethe second end 4 of the measurement optical fiber 2, 3 to be reflective.The frequency of the events measured by the detector device enables thedose received by the measurement optical fiber to be calculated. Sincethe measurement of an event in a first direction and the measurement ofthe same event in a second direction cannot be caused to coincide inorder to evaluate the point at which the event took place, it ispreferred to use a statistical method as described below.

If a multi-channel detection device is used, such as a multi-anodephotomultiplier tube (MAPMT), there is also the problem of considerablegain dispersion amongst the channels. The gain of each electronicchannel associated with the MAPMT may be initially adjusted (once andforever, or periodically, or prior to each utilization, for example) soas to make the level of a photoelectron signal uniform by fixing anidentical discrimination threshold level for all of the electronchannels.

FIG. 2 shows a first embodiment of the dosimeter of the invention. Afirst set of measurement optical fibers 2 of diameter d_(y) are alignedalong a first direction X of the dosimeter at a pitch, e.g. a constantpitch, of L_(y). These first measurement optical fibers are disposedbetween two sheets of a material 12, e.g. a reflective material, servingto hold the optical fibers. The component as prepared in this way is inturn placed between two sheets of an optically-insulating material 13.This operation is repeated in a second direction Y of the dosimeter forthe second measurement optical fibers 3 of diameter d_(x), and at aspacing or pitch L_(x). The two resulting components are thensuperposed, e.g. so that the first optical measurement fibers and thesecond optical measurement fibers form between them an angle of about90°. As shown in FIG. 2, it is also possible to remove one of the sheetsof optically-insulating material 13 that lies between the two layers ofmeasurement optical fibers. The dosimeter as built up in this way iscompletely X-ray transparent, which is an essential condition forenabling such a dosimeter to be used so as to ensure that it does notimpede the practitioner during intervention. Nevertheless, thesemeasurement fibers are not necessarily disposed in two separate planes,and they could, for example, constitute a single plane of woven fibers.

FIG. 3 shows the path followed by optical information from detection bythe measurement optical fiber until the detector 9 is reached. Inparticular, it is necessary to connect the measurement optical fibers 2,3 at their first ends 5 to the clear optical fibers 6 which extend them,with the connection being made by means of adhesive, for example, or byany other bonding means enabling optical information to be transmitted.The first ends 5 of the measurement fibers 2, 3 and the first ends 14 ofthe clear fibers 6 are polished and they are placed facing one anotherin pairs so as to be stuck together with an optical adhesive ofrefractive index close to that of the material used in the opticalfibers. In order to ensure that the cores and the cladding of the fibersare accurately aligned during the application of adhesive, each pair offibers may be held in a tube or “ferrule” of Teflon or other rigidmaterial, which then remains permanently in position in order toguarantee a mechanically robust optical connection. The second end 15 ofeach clear fiber 6 where it is inserted in an orifice 8 of the adapter 7can likewise be polished and the surface of the second end 15 of eachoutputting clear fiber 6 can be bonded with adhesive so as to ensureproper optical coupling with the plane inlet window of the detector.

The second end 4 of each measurement optical fiber 2, 3 may also beconnected to a second clear optical fiber 6 in similar manner.Naturally, under such circumstances, the second end 4 of eachmeasurement optical fiber 2, 3 is neither optically closed norreflective. The second end 15 of each second clear fiber can then beplaced facing a cell of the detector 9 in the manner defined above. Foreach given measurement fiber 2, 3 this second end may alternatively beplaced close to the second end 15 of the first clear fiber 6 whose firstend 14 is connected to the first end 5 of a given optical fiber 2, 3,such that the signals coming from the first and second clear fibers 6connected to the same measurement fiber 2, 3 are added together by thedetector.

It may be necessary to evaluate the dispersion in the responses of thedetection channels of the device. Although the characteristics of themeasurement fibers 2, 3 and of the clear fiber 6 are guaranteed topresent little dispersion, the reproducibility of the quality of theoptical bonding between them needs to be studied, as does the dispersionof the channels of the detector device. For given radiation flux, thecount rate of each detection channel differs as a function of thefollowing:

-   -   the intrinsic dispersion between the measurement fibers 2, 3;    -   the quality of the optical bonding between the measurement        fibers 2, 3 and the clear fibers 6;    -   the quality of the fiber cladding; and    -   the dispersion of the channels of the detector device when using        a multi-channel detector device.

To calibrate the device of the invention, a known portion 24 of eachmeasurement fiber 2, 3, e.g. a portion situated directly upstream fromits first end 5 where the measurement fiber 2, 3 is bonded to a clearfiber 6, is subjected to radiation coming from a radiation source undervoltage V and current I, thus corresponding directly to a known dosevalue f previously measured by conventional means such as an ionizationchamber (not X-ray transparent). By measuring the count frequency C⁰_(k) at the output from the detector device, it is thus possible toestablish a correlation for each fiber between the dose received by thedetector portion 24 of each measurement fiber k and the measuredfrequency. Once calibration has been performed, the set of area dosagevalues per count unit F⁰ _(k)=f/C⁰ _(k)*sc, corresponding to a givenfiber k or to a fiber and multi-channel detector channel in association,is stored in a control unit 22. The term sc represents the equivalentarea of the detector fiber. Depending on the type of detector used, themeasured energy or some other parameter, particularly count frequency,may optionally be associated with the received dose. These calibrationoperations, which are performed during the design of the installation ofthe invention, need be performed subsequently only occasionally, e.g.during maintenance operations on the installation.

In addition, each associated optical fiber and detector channel can becalibrated separately by calibrating firstly the optical fibers byplacing a single detector to face each of the second ends 15 of theclear fiber 6, e.g. a single-celled detector. Furthermore, the channelsof the multi-cellular detector can be calibrated separately, e.g. bycausing each channel to measure a known given signal. The calibrationvalue F⁰ _(k) for an optical fiber and the associated detector channelis then obtained by combining the value obtained for the fiber on itsown with the value obtained separately for the facing channel of thedetector. By way of example, this approach makes it possible, in use, toreplace one or other of these two pieces of equipment, should it befound to be defective, without it being necessary to replace both ofthem.

Since the measurement fibers 2, 3 have known characteristics, if it isknown that the radiation dose has been received at a distance d from thedetector portion 24 of the measurement fiber k along said fiber, it ispossible to determine the count that would have been measured if thedetection had occurred in said detection portion 24 on the basis of thecount measured at the output from the detector, and using theattenuation length λ_(att) of the measurement fibers in application ofthe following formula:

$C_{k}^{d} = {C_{k}^{0}{\mathbb{e}}^{- {(\frac{d}{\lambda_{att}})}}}$

FIG. 4 shows an embodiment of a installation implementing the method ofthe invention. The dosimeter 1 is constituted by two crossed planes eachof 32 scintillating fibers having a diameter of 1 millimeter (mm), wovenat a pitch of 10 mm, thus covering a detection area of about 310 mm×310mm. The pitch is representative of the resolution of the resulting dosemap, and the selected detection area is representative of theinvestigation zones used in applications of this type, but these twoparameters can naturally be modified. The scintillating fibers 2, 3 usedin the dosimeter are of doped polystyrene with two claddings. Forexample, it is possible to use “blue” Polifi 02 44-100 fibers fromPOL-HI-TECH, Italy, having an emission spectrum centered on 438nanometers (nm) and a mean attenuation length of 500 mm, with a decaytime of 2.3 nanoseconds (ns). It is also possible to use “green” Y11(175) MJ non-S scintillating fibers from Kuraray, Japan having anemission spectrum centered on 500 nm, a mean attenuation length of 900mm, and a decay time of 7.1 ns, or any other type of fast measurementfiber, whether or not it is made of polystyrene. In this type ofapplication, the use of polystyrene is justified because it has densityclose to that of the skin, and because of its high degree offlexibility. In this case, the component 12 is made of mylar presentinga density of 1.35 grams per cubic centimeter (g/cm³), and is made up ofsheets having a thickness of 0.045 mm. In this example, theoptically-insulating component 13 is black polycarbonate, having densityof 1.2 g/cm³, and implemented in the form of sheets having a thicknessof 0.015 mm. An epoxy adhesive is used for bonding together themeasurement optical fibers 2, 3 and the sheets 12 and 13. The totalthickness of the resulting detector is about 2.4 mm.

To obtain greater flexibility for the dosimeter, and to enable theradiation dose received by regions having a short radius of curvature tobe evaluated, it is possible to use measurement fibers 2, 3 of smallerdiameter, and consequently clear fibers 6 of corresponding size andorifices 8 of corresponding size in the adapter 7. Instead of beingstuck between sheets, the measurement fibers 2, 3 may alternatively beincorporated in a molding, e.g. of black resin.

Each measurement optical fiber 2, 3 is about 310 mm long, and it isbonded to a polystyrene clear fiber, e.g. of the Kurakay type having asingle layer of cladding, a length of about 1400 mm, and a diameter ofabout 1 mm, with the first ends 5 of the measurement fibers 2, 3 and thefirst ends 14 of the clear fibers 6 being initially polished withabrasive powder, initially of grain size 600P and subsequently 1200P. Byway of example, the clear fibers 6, which are long, may alternatively befibers made of quartz that possess better transmission, or fibers madeof polymethyl methacrylate (PMMA), or other fibers. In this example,only one clear fiber 6 is used per measurement fiber 2, 3, but in analternative it would be possible to connect each measurement fiber 2, 3to a clear fiber at each of its ends 4, 5 as explained above. The freeends of the 64 clear fibers are grouped together on an adapter which isa mechanical part made of black plastics material and pierced by 64holes each having a diameter of about 1.05 mm and at a pitch of 2.3 mm.It is thus possible to obtain an 8×8 matrix of clear fibers 6 placedfacing cells 10 of the detector 9, which in this example is a MAPMTphoto multiplier having 64 channels and supplied under the referenceHamamatsu H7546 MOD. This detector has an inlet window measuring about20 mm×20 mm. To provide lighttightness for the clear fibers 6, assumingthey are not optically insulated, it is possible to envelop them inblack polycarbonate sheathing, or in black polyethylene, or the like.Under such circumstances, each fiber may have a diameter that is smallerthan the diameter of the associated scintillating fiber 2, 3 such thateach assembly comprising a clear fiber and a sheath presents a diameterof the same order as the diameter of the associated scintillating fiber.The MAPMT detector is fitted with integrated analog electronics (two32-channel chips) with sensitivity at the level of a fraction of aphotoelectron. Each electron channel includes a discriminator with aprogrammable threshold for delivering a digital signal that is used bybeing counted up to a frequency of 10 megahertz (MHz).

The flexible and light-tight dosimeter 1 is for placing against the bodyof the person under examination. In FIG. 4, the dosimeter is thus placedunder the body of the patient between the radiation source 18 and thepatient 16. The dosimeter is placed in register with the inlet face ofthe radiation beam 11, e.g. an X-ray beam, as produced by a tube 18situated on a moving cradle (not shown). The emitted X-ray beam may beemitted in pulsed form, in which case the detector device can besynchronized by performing detection for each X-ray pulse, withcalculations being performed between two given pulses. For example,during an interventional radiological examination performed using anX-ray apparatus operating in pulsed mode, with pulses having a durationof about 7 milliseconds (ms) and being repeated once every 40 ms, thedetector can be supplied with a synchronizing signal of the sameduration as an X-ray pulse, thereby causing counting to be performed onthe fibers during exposure. The time available between takingmeasurements (of the radiation) is then used for reading the individualcount registers, for storing the data, for calculating the dose receivedper unit area at each of the points (i, j) of the dosimeter, and thus bythe irradiated organ, and for updating the display.

If the X-ray beam X is emitted continuously, detection can still beperformed during a time td and calculation during a time t_(c) inperiodic manner giving a period T=t_(d)+t_(c), with the total radiationbeing determined by comparing the calculated dose received during theduration td with the dose received throughout the duration T, e.g. bysimple proportionality.

The transmitted X-ray beam may also be detected by a detector 19 whichtransmits radiological information to a central unit 22. In addition,the dose passing through each measurement fiber 2, 3 of the dosimeter 1,and thus reaching the object under examination, is transformed intooptical information conveyed via the clear fibers 6 to the multi-channeldetector 9. The signals coming from the photomultiplier MAPMT areprocessed therein by two integrated circuits each having 32 channels.After the signals have been shaped, this circuit is capable ofdelivering sequentially (channel after channel) the charge collected oneach anode of the MAPMT by means of a signal of amplitude that isproportional to said charge, and thus to the detected radiation inapplication of the calibration values F⁰ _(k) stored in the control unit22. This output signal is digitized by an analog-to-digital converter(ADC), e.g. contained in the central unit 22, so as to provideinformation that can be displayed on a monitor screen 20. The circuitalso provides a logic signal that is activated each time a photoelectronis produced at the photocathode of the MAPMT. Measuring the frequency ofthis logic signal enables the activity of each channel to be measured,and consequently serves to measure the quantity of radiation picked upby each of the measurement optical fibers 2 extending in rows in a firstdirection of the dosimeter and the measurement optical fibers 3extending in columns in a second direction of the dosimeter. Since thelogic signal is the sum of the signals associated with each channel, itis possible to measure individually the activity of a selectedmeasurement optical fiber 2, 3 by inhibiting all of the channels otherthan the selected channel so as to conserve only the frequencycorresponding to the selected measurement optical fiber. This sameoperation is then performed on each of the channels, thus leading to theindividual measurement of the dose received by each of the fibers.

Alternatively, a logic signal may be associated with each channel, thusenabling counts to be measured simultaneously on all of the 32 channelsfor each pulse of the X-ray beam.

On the basis of the frequencies R_(i) and C_(j) measured respectively onthe row i and the column j of the dosimeter, a first estimate of thedose D_(ij) per unit area received at the point having coordinates (i,j) of the dosimeter can be obtained in application of the followingformula:

$D_{ij} = {\frac{R_{i}}{F_{i}^{0}} \times \frac{C_{j}}{\sum C_{k}} \times {\mathbb{e}}^{\frac{d_{ij}}{\lambda_{att}}}}$where d_(ij) is the distance of the fiber j from the first end of thefiber i.

By symmetry, it is possible to obtain a second estimate of the dose perunit area D_(ij) received at the same point in application of thefollowing formula:

$D_{ij} = {\frac{Cj}{F_{j}^{o}} \times \frac{R_{i}}{\sum R_{k}} \times {\mathbb{e}}^{\frac{d_{ji}}{\lambda_{att}}}}$where d_(ji) represents the distance of the fiber i from the first endof the fiber j.

Naturally, during a measurement, the sum over all of the rows of themeasured counts is equal to the sum over all of the columns of themeasured counts and corresponds to the total intensity.

It is possible to use one, or the other, or a weighted average of thesetwo values to estimate the dose per unit area received at the point (i,j) under consideration. The calculated values are then shown on thescreen 20, and this is done at a speed that is fast enough to enable thedata on the screen 20 to be refreshed quickly. In addition, since thecutaneous dose per unit area D_(ij) is calculated in two different ways,it is possible to monitor measurement reliability and to detect possiblefailure of the dosimeter by comparing the two values. Thereafter, if itis desired to use measurement fibers of better quality in one of thedirections of the dosimeter while retaining measurement fibers of lowerquality in the second direction, so as to avoid increasing productioncosts excessively, it is possible to weight the results obtained bycalculation performed on the basis of the frequency measurement obtainedfrom the higher performance fibers, so that this number is preponderantin the result obtained.

The frequency of the logical signal (directly associated with the dosereceived by each measurement optical fiber) is counted in a fieldprogrammable gate array (FPGA) type circuit. A digital signal processor(DSP) performs the following operations:

-   -   managing the high voltage of the MAPMT, as generated locally by        a compact Hamamatsu CA 4900-01 module;    -   configuring the integrated circuits;    -   reading the temperature of the unit; and    -   communicating with the control unit.

This communication with the control unit 22 consists in regularlyreassessing the count data so as to refresh the display on the screen20, enabling the user 21 to define operating parameters, such asutilization mode, MAPMT voltage, or sensitivity level of the electroniccards, etc.

It is thus possible for the user 21 to monitor in real time on thescreen 20 a map of the cutaneous radiation dose, both in terms ofaccumulated dose and in terms of instantaneous dosage rate for eachexposed zone. The control unit 22 or the user 21 can then take accountof the information displayed on the screen 20 in determining how therapyis to progress. If the accumulated cutaneous radiation dose in a regionor over the entire irradiated extent exceeds a certain pre-establishedthreshold, the control unit can be arranged to trigger an alarm, forexample. During the operation, the X-ray beam 11 may optionally bereorientated or moved by the user 21, e.g. in the event of the personunder examination 16 moving on the examination table 23. Such movementmay be forwarded automatically to the central unit 22 or it may be inputas a parameter by the user 21. In the event of a large movement, it canbe necessary to modify the parameters specific to each measurementoptical fiber 2, 3 since they might have been calibrated for only agiven set of positions of the radiation source.

In addition, the received radiation doses may be coupled with a databasefor long-term monitoring of the person under examination, possiblyassociated with studying the effects of that person's exposure to theradiation, and with the irradiated zone being accurately identifiedrelative to the anatomy of the person under examination, during eachoperation.

FIG. 5 shows a second embodiment of an installation implementing themethod of the invention. In this case, the dosimeter 1 is incorporatedin the examination table 23 so as to cover all postero-anteriorincidences of X-rays to which a person under examination might besubjected. The pitch of the measurement fibers 2, 3 may optionally beadapted accordingly. Thus, a plurality of dosimeters may be integratedin the examination table in register with those portions of the bodythat are the most investigated, and they may be connected simultaneouslyor successively to a common detector device. Such a “whole body”dosimeter integrated in the examination table and covering practicallyall of its surface area can be used on its own or in association withadditional “surface” dosimeters that are not integrated and that areused in the manner shown in FIG. 4. Such a device may be advantageous inthe fields of interventional radiology and conventional orinterventional tomography. Such an examination table 23 may contain aplurality of housings suitable for receiving integrated dosimeterseither simultaneously or in succession.

1. A method of measuring in real time a radiological radiation doseabsorbed by a region under inspection subjected to a flux ofradiological radiation, the method comprising the steps consisting in:a) detecting the incident radiation at at least one point of the regionunder inspection using an X-ray transparent dosimeter comprising atleast a first bundle of measurement optical fibers containing at leastone fiber placed in said region under inspection and adapted to generatea light signal on receiving radiological radiation; b) measuring saidlight signal away from the region under inspection after it has beentransmitted along the measurement optical fiber; and c) determining thedose of radiological radiation received by said measurement opticalfiber on the basis of said light signal and a position where theradiological radiation is detected along said measurement optical fiber,the dose of radiological radiation received at said position beingcalculated as a function of at least one parameter F⁰ _(k) specific tosaid optical fiber.
 2. A method according to claim 1, in which at leastone parameter F⁰ _(k) is obtained by a preliminary calibration stepduring which a dose of radiation is detected at at least one point ofthe region under inspection by means of a radiation detector that is notX-ray transparent.
 3. A method according to claim 1, in which step b) isperformed using a detector device comprising at least one cell, and inwhich the parameter F⁰ _(k)takes account of at least the optical fiberand at least one cell of the detector device associated with said fiber.4. A method according to claim 1, further comprising a step d)consisting in emitting an alarm signal if the accumulated receivedradiation dose exceeds a pre-established threshold.
 5. A methodaccording to claim 1, further comprising a step e) consisting indisplaying on a screen the dose of radiation received at least one pointof the region under inspection.
 6. A method according to claim 5,further comprising a step f) consisting in detecting the radiationtransmitted through the region under inspection, and in displaying on ascreen a radiographic image as detected in this way.
 7. A methodaccording to claim 6, in which the radiographic image obtained in stepf) and the image of the received radiation dose as obtained in step e),are displayed on the same screen.
 8. A method according to claim 1, inwhich at least steps a), b), and c) are repeated for a plurality ofpoints of the region under inspection, enabling a map to be obtained ofthe dose received by the region under inspection.
 9. A method accordingto claim 1, in which at least steps a), b), and c) are repeated for aplurality of measurement time intervals enabling time variation in thedose received at at least one point of the region under inspection to beobtained.
 10. A method according to claim 9, in which the radiation isgenerated by a pulsed source, and the repetition of at least steps b)and c) is synchronized with said source.
 11. A method according to claim1, in which at least steps a), b) and c) are performed for at least twoangles of incidence of the radiation, and in which combined use is madeof the received radiation doses as determined in step c) for each of theangles of incidence.
 12. A device for real-time measurement of a dose ofradiological radiation absorbed by a region under inspection subjectedto a flux of radiological radiation, the device comprising: an X-raytransparent dosimeter comprising at least a first bundle of measurementoptical fibers containing at least one fiber placed in said region underinspection and adapted to generate a light signal on receivingradiological radiation in order to detect the incident radiation atleast one point of the region under inspection; measurement means formeasuring said light signal away from the region under inspection afterthe light signal has been transmitted along the measurement opticalfiber; and means for determining the dose of radiological radiationreceived by said measurement optical fiber on the basis of said lightsignal; and in which the light signal is transmitted to a detectordevice used for measuring it, transmission taking place along themeasurement optical fiber used for detecting the radiation, said fiberhaving a first end, and along at least one clear optical fiber extendingfrom a first end of the clear fiber that is connected to the first endof the measurement optical fiber to a second end of the clear fiber,which second end is placed facing the detector device, and in which themeans for determining the dose of radiation received at said point ofsaid measurement optical fiber comprise a control unit containingparameters that are specific to the optical fibers used.
 13. A deviceaccording to claim 12, in which each measurement optical fiber iscomprised between two optically-insulating sheets.
 14. A deviceaccording to claim 12, in which each measurement optical fiber is moldedin a reflective resin comprised between two optically-insulating sheets.15. A device for real-time measurement of a dose of radiologicalradiation absorbed by a region under inspection subjected to a flux ofradiological radiation, the device comprising: an X-ray transparentdosimeter comprising at least a first bundle of measurement opticalfibers containing at least one fiber placed in said region underinspection and adapted to generate a light signal on receivingradiological radiation in order to detect the incident radiation atleast one point of the region under inspection; measurement means formeasuring said light signal away from the region under inspection afterthe light signal has been transmitted along the measurement opticalfiber; and means for determining the dose of radiological radiationreceived by said measurement optical fiber on the basis of said lightsignal; and in which the first fiber bundle is disposed along a firstdirection and in which the dosimeter further comprises a second bundleof optical fibers comprising at least one second measurement opticalfiber disposed in a second direction forming an angle with the firstdirection.
 16. A device according to claim 15, in which each measurementoptical fiber is comprised between two optically-insulating sheets. 17.A device according to claim 15, in which each measurement optical fiberis molded in a reflective resin comprised between twooptically-insulating sheets.
 18. A device for real-time measurement of adose of radiological radiation absorbed by a region under inspectionsubjected to a flux of radiological radiation, the device comprising: anX-ray transparent dosimeter comprising at least a first bundle ofmeasurement optical fibers containing at least one fiber placed in saidregion under inspection and adapted to generate a light signal onreceiving radiological radiation in order to detect the incidentradiation at least one point of the region under inspection; measurementmeans for measuring said light signal away from the region underinspection after the light signal has been transmitted along themeasurement optical fiber; and means for determining the dose ofradiological radiation received by said measurement optical fiber on thebasis of said light signal; and in which at least one bundle of opticalfibers is integrated in an examination table.
 19. A radiologicalinstallation comprising: an X-ray transparent dosimeter comprising atleast one bundle having at least one measurement optical fiber placed ina region under inspection, and adapted to generate a light signal onreceiving radiological radiation, so as to enable the incident radiationto be detected at least one point of said region under inspection;measurement means for measuring said light signal away from the regionunder inspection after it has been transmitted along the measurementoptical fiber; and means for determining the dose of radiologicalradiation received by said measurement optical fiber on the basis ofsaid light signal, and further comprising: a radiation generator; aradiographic detector; and means for displaying the radiation dosereceived, said means also enabling radiographic images to be displayedof the region under inspection as supplied by the radiographic detector;an examination table; and wherein said at least one bundle ofmeasurement optical fibers is integrated in the examination table. 20.An installation according to claim 19, further comprising at least oneadditional device that is not integrated in the examination table, forreal-time measurement of a dose of radiological radiation absorbed by aregion under inspection subjected to a flux of radiological radiation,the additional device comprising: at least an additional first bundlecomprising at least one additional first measurement optical fiberplaced in said region under inspection and adapted to generate anadditional light signal on receiving radiological radiation, in order todetect the incident radiation at least one point in said region underinspection; additional measurement means for measuring said additionallight signal away from the region under inspection after it has beentransmitted along the additional measurement optical fiber; andadditional means for determining the dose of radiological radiationreceived by said additional measurement optical fiber on the basis ofsaid additional light signal.
 21. A method of measuring in real time aradiological radiation dose absorbed by a region under inspectionsubjected to a flux of radiological radiation, the method comprising thesteps consisting in: a) detecting the incident radiation at at least onepoint of the region under inspection using an X-ray transparentdosimeter comprising at least a first bundle of measurement opticalfibers extending in a first direction and containing at least one fiberplaced in said region under inspection and adapted to generate a lightsignal on receiving radiological radiation, and a second optical fiberbundle containing at least one second measurement optical fiber adaptedto generate a light signal on receiving radiological radiation, andextending along a second direction forming an angle with the firstdirection; b) measuring said light signal away from the region underinspection after it has been transmitted along the measurement opticalfiber; and c) determining the dose of radiological radiation received bysaid measurement optical fiber on the basis of said light signal.
 22. Amethod according to claim 21, in which steps b) and c) are performed,for at least one overlap point between a first measurement optical fiberof the first bundle and a second measurement optical fiber of the secondbundle, on the basis of the radiation detected at least by the firstoptical fiber of the fibers of the first bundle, of the radiationdetected by the second optical fiber, and of the position of saidoverlap point along the second optical fiber.
 23. A method according toclaim 21, in which the steps b) and c) are performed, at least for anoverlap point between a first measurement on the basis of the radiationdetected at least by the second optical fiber of the fibers in thesecond bundle, of the radiation detected by the first optical fiber, andof the position of said overlap point along the first optical fiber.